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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 9 |
| 3 | 18 |
| 4 | 162 |
| 5 | 648 |
| 6 | 4050 |
| 7 | 20412 |
| 8 | 117369 |
| 9 | 639576 |
| 10 | 3628233 |
| 11 | 20360970 |
| 12 | 115858512 |
| 13 | 659144304 |
| 14 | 3772679976 |
| 15 | 21637128240 |
| 16 | 124518397770 |
| 17 | 718139766240 |
| 18 | 4151542099770 |
| 19 | 24045292507860 |
| 20 | 139520453553468 |
| 21 | 810834881716080 |
| 22 | 4719151317787452 |
| 23 | 27502373918849544 |
[1,0,9,18,162,648,4050,20412,117369,639576, 3628233,20360970,115858512,659144304,3772679976, 21637128240,124518397770,718139766240, 4151542099770,24045292507860,139520453553468, 810834881716080,4719151317787452, 27502373918849544] |